This disclosure is directed to a method and apparatus for cleaning a pipeline. More particularly, it is intended for cleaning a pipeline which has an accumulated coating of paraffin in the line. Even more specifically, it is intended for the progressive removal of paraffin coatings in the pipeline during continued use in operation of the pipeline so that the pipeline need not be shut down. Rather, the cleaning is carried out utilizing the fluid drive from pumping oil based materials through the pipeline giving rise to the paraffin coating.
Cleaning pipelines is believed to be well known and is done as a regular matter for maintaining pipeline flow capacity. The coatings which form in a pipeline differ dependent on a number of factors. For instance, fresh water normally carries mineral constituents which will plate out and form a kind of hard crust. In those portions of the country where the water is highly mineralized, the coatings form a type of boiler scale which is accreted over a period of time to thereby close off the ID of the pipe generally uniformly by forming an every thickening deposit. It is typically carbonate which builds up a chalky deposit which is a fairly brittle adherent layer. It can build up to the point where the pipeline is nearly completely plugged. This normally builds up over a long period of time, thereby resulting in a deposit which somewhat resembles gypsum board, sheetrock or the like. The primary difference is that it is concentrically circular in shape.
In water lines which deliver cooling water from the ocean or other bodies of water which have living cells therein, it is also not uncommon for the cells to deposit in the line and place such deposits in the line to reduce the flow capacity. Such deposits can range from oyster shells to barnacles and other living organisms which may live in salt water, brackish water and many of which even live in fresh water. Both types of deposits mentioned above have certain advantages, namely primarily that they are hard, and can even be brittle. The present disclosure is directed to cleaning soft paraffin from a line in circumstances where heavy molecules coat out from a flow of oil produced from a formation or a well which connects with several gathering lines which form a field line extending to a processing plant. Oil produced from a well typically includes constituents having a generalized paraffin series formula of C.sub.n H.sub.2n+2. In the foregoing n is a whole number positive integer. Where n is under three or four, the molecule defined thereby is normally gaseous at room temperature. Eventually, where n increases over about six or seven, that molecule tends to liquify, and where n increases further, the molecule will ultimately solidify. For the larger weight molecules in a stream of oil from a formation, there is a tendency to solidify. A paraffin type coating is often formed in a gathering line. Coating is dependent on many factors including the temperature of the exterior of the line, the temperature of the produced oil, the mix of the constituents of the paraffin series in the flow, and many other similar factors. Suffice it to say, there is a generalized pattern in which paraffin coatings are formed in the pipeline.
A paraffin coating should be contrasted with the type of coating which collects on the interior of water lines. Those coatings are quite hard having the consistency of sheetrock in many instances. Those coatings are somewhat brittle compared with paraffin coatings. Paraffin coatings are more like a heavy grease or wax which will maintain a shape but which is not brittle and which can be smudged but not broken. Pipeline cleaning is altogether a different problem with a paraffin coating that is soft and resilient compared with a brittle coating formed of carbonates in a water line. Cleaning is therefore materially altered.
Consider a pipeline which requires cleaning. Assume that the coating is somewhat thin and may or may not include rust or mill scale on the pipe, and some deposit of relatively thin nature on the interior of the pipe. Pigs made heretofore have approached that problem primarily with scratching members such as tungsten carbide particles imbedded on the exterior surface. Another type of pig includes wire bristles arranged in stripped patterns around a pig body. Generally, the pig bodies have been relatively stiff to hold or support the sharp points deployed around the exterior of the pig against the pipe so that small chisel like points cut the coating and ultimately clean the pipeline. Many pigs heretofore have been provided with a relatively stiff body with extremely sharp numerous points such as the bristles or tungsten carbide particles mentioned above.
The present disclosure sets forth a pig for cleaning soft coatings at the opposite extreme. Light weight pigs have been known heretofore, but the pig of the present disclosure is a two foam pig which has a central core and an outer foam body. The outer foam body is extremely light in material. That is, it is preferably formed of an open cell foam weighing between about one and four pounds per cubic foot. It is fabricated full gauge, that is, the cylindrical foam body has a diameter equal to the ID of the pipeline to be cleaned. A small concentric passage is formed in the foam body and a slightly heavier foam is placed in that passage. This defines an elongate central stiffening member which is only slightly stiffer but which is nevertheless sufficient to provide some body and structural integrity to the pig. This enables the pig to maintain a full gauge profile thereby totally plugging the pipeline and enabling the fluid drive through the line to force the pig along the pipeline. Moreover, it is sufficiently light in structure that it may deform when encountering the soft paraffin build up. On repeated passes, the size of the pig remained unaltered, but nevertheless, the central portion is made larger. That is to say, the slightly stronger, stiffer foam becomes larger, enabling the pig body to remain structurally intact and to thereby push the paraffin along the line. The paraffin does not break, fracture or tear free from the wall of the pipe in the same fashion as does deposited carbonates in water lines. Rather, the paraffin is dislodged in a different fashion. This difference causes the paraffin to ultimately emerge from the pipeline after having been shaped and reshaped when pushed through the pipeline. On this basis, the paraffin has a different shape resulting from a detachment mechanism. The pig is able to ride over tough lumps of paraffin adhering to the pipeline. They might be smudged or smeared as the pig deforms in riding over the deposits. In any event, multiple passes by a sequence of pigs having a steadily larger central portion in the pig enables the pigs to break loose or dislocate the paraffin as a pliable resilient body in a sequence which prevents line plugging. Line plugging is thus avoided, and the pigs are sequentially retrieved along with pieces of paraffin which break free. After multiple passes, the last pig through the pipeline can be formed with a central reinforcing so that most of the paraffin in the line can be cleaned and forced from the line. When this is completed, the line then at most has only a thin layer of paraffin of relatively uniform thickness left on the wall of the pipe, at which time stiffer bodied pigs with more aggressive bristles or scraping attachments can be used. This prepares the pipeline for the last cleaning step.
The foregoing sets forth a pig and a method of cleaning paraffin coated pipelines. More details will become more readily apparent on consideration of the below written specification which considered in conjunction with the drawings sets forth both the apparatus and method of use. Other details will be understood at this juncture.